The temporary chief constable of Wiltshire Police Kier Pritchard saw Nick Bailey and his wife at the intensive care unit and said:

"He's well, he's sat up. He is not the Nick that I know but of course he's receiving a high level of treatment. He's in the safe hands of the medical professionals working in Salisbury District so I'm very confident he's getting the best professional support that he can.

"Of course he's very anxious, he's very concerned. He did his very best on that night.

"I've known Nick for many years, he's a great character, he's a huge presence in Wiltshire Police - well liked, well loved, a massively dedicated officer. He's clearly receiving high specialist treatment.

"All of our staff that attended the incident in Salisbury in the Maltings, they performed the role that police officers and police staff do every day up and down the country. (With) limited information, (we) responded to try and protect people and safeguard people who we knew were ill.

"I'm massively proud of what Nick did and all of my staff on that night, they did a first-class job."

The police cordon outside Mr Skripal's home was widened following a flurry of activity.

A large blue forensic tent was set up on the street as more police and incident support vehicles arrived from South Western Ambulance Service. Officers extended the cordon to seal off the whole of Christie Miller Road, although residents and their vehicles are allowed to come and go.

Police cordons have also been put up around the gravestone of Mr Skripal's wife Liudmila, who was buried in 2012, and the memorial stone of his son, Alexander, who was cremated last year.

They are located at separate sites in the London Road Cemetery and are each guarded by a police officer.

A police officer stands guard at the London road cemetery in Salisbury where the wife and son of Sergei Skripal are buried on March 8, 2018 (Image: Ben Stansall/AFP/Getty Image)

Prime Minister Theresa May told ITV News: "First of all the police are still investigating, obviously, we need to let the police have the space and time to conduct their investigating so that we get the best possible evidence of what has happened in this particular case.

"Of course if action needs to be taken then the Government will do that. We'll do that properly, at the right time, and on the basis on the best evidence."

Asked whether the action taken if Russia was found to be responsible could include the expulsion of its ambassador, Mrs May responded: "We will do what is appropriate, we will do what is right, if it is proved to be the case that this is state-sponsored.

"But let's give the police the time and space to actually conduct their investigation."